Extreme pressure lubricating grease



Patented Jan. 1, 1952 EXTREMEPRESSURE LUBRICATING GREASE Arnold J. Morway,

Clark Township, and John J. Kolfenbach, Somerville, 'N. J

., .assignors to Standard Oil Development Company, a corporation of Delaware Application August 31, 1949, Serial No. 113,302

14 Claims.

The present invention relates to extreme pressure lubricating greases and particularly to lubricating greases consisting of a lubricating oil thickened to-agrease consistency with a combination of the usual metal soaps of higher fatty acids combined with alcw molecular weight meta1 salt. The invention is particularlyconcerned with a lubricating grease composition, and a process-of preparing the same, which comprises a conventional lubricating oil, "a conventional high molecular weightmetal soap, anda low molecular weight salt of a sulfur-bearing heterocyclic acid. The present application .is a continuation-in-part of an application 'filed by the present inventors on November 17, 1948, Serial No. 60,615, now U. S. Patent-2,516,137, issued on July 25, 1950.

As described in said co-pending application Serial'No. 60,615 certain heterocyclic aldehydes may be reacted with strong bases to produce the well known Cannizzaro reaction by which one molecule is reduced to the alcohol, The base molecule of aldehyde is oxidized .to the acid while asecond molecule is reduced to'the'alcohol. The base used, "of course, reacts promptly with the acid produced to form the salt, but'the alcohol is n t reacted'to any substantial degree.

As pointed out in said application, lubricating greases which contain a complex composition or mixture of ordinary soaps'of higher fatty acids combined with low molecular weightmetal salts of acids resultingfrom the Cannizzaro reaction have exceptionally good 'high temperature properties. The proportions of the soap and salt may be varied rather widely, but, in general, 1 to 3 molar parts of the soap should be combined with 1 to 3 molar parts of the salt which results from the Cannizzaro reaction. As the Cannizzaro reaction proceeds and the alcohol is released, the alcohol may, under some conditions, be polymerized to a relatively non-volatile product. The volatile constituents, mainly themonomerlc alcohol and water produced during .saponification or neutralization of the -acids,.are ordinarily removed ;from the grease during the grease cooking operation.

The present invention is based upon the discovery of exceptional and desirable properties of the salts ofsulfur-containing heterocyclicacids such as those derived from the ithiophene and homologous and analogous aldehydes subjected to the Cannizzaro reaction. In general, these aldehydes are of the five-membered heterocyclic ring type, with a molecular weight below about 200, as a maximum. The thiophene aldehydes, with sulfur forming one member of the five membered ring are preferred butrcompoundsincluding an oxygen atomin'thering with-sulfur attached elsewhere are also useful, e.g. the thiofurfurals. .Nitrogenebearing :heterocyclic ring compounds also are usefuLprovidedthey contain sulfurand are reactive in the Gannizzaroreaction.

In proportions by weight, greases prepared according to the presentinvention ordinarily will contain about 5 to 25% by weight of the metal soap, preferably the alkali metal soap, of fatty acids having an average of not less than 1 2 nor morethan 22..carbon atoms. Theywill also contain about 3 :to 215% by weight ofzthe non-volae tile reaction product m" the Cannizza-ro reaction. By the expression.nonevolatile reaction product, it is intended to cover-the salt which 'resultsfro'm the acid formed as mentioned above, plus the relatively non-volatile monomeric or polymerized alcohols or other by-products of the reaction which remain in the compositionafter cooking-the grease-forming. temperature of about 300 to 450 'F. 0r more. The thiophenecarbinol (alcohol) :monomeris much higher boiling than furfurylaico'hol (404 .vs .338" E). It is alsoin soluble in waterand does :not:form a constantboiling mixture (although a portion may steam distill) Thus :the usual maximum temperature of manufactureof the grease would not distill out the .thiophenecaribinol. However,..the sulfur! bearing alcohol does ;not adversely eafiect the grease structureasedoesaa significantamount of furfuryl alcohol. For this reason :the :sulfurbearing alcohols may he desirably left in the grease which is. notrtrue of furfuryl alcohol.

The proportions mentioned above. are based. on the Weight of the final composition. -Mineral base lubricating oil is preferred as the liquid constituent of the grease, but synthetic oils may be used .so far asthey are compatible withxthe soap-forming and lower acid 101'- salt-formingoperations. Ordinarily, .itis preferable to conduct at least the soapandsalt-forming reactions in the presence ofinertlubrioating oils of'the hydrocarbon or mineral base type, but non-hydrocarbon oils such a synthetic esters, polyglycols, and the like, may be substituted for any part of the additional oil after the soap and salt-forming operations have been completed. This is known in the prior art.

The preferred salts of the sulfur-bearing heterocyclic acids are those prepared from the alkali metal hydroxides, especially sodium hydroxide, which is generally preferred because of its availability and because it makes a firm grease that is relatively water resistant. Lithium hydroxide may be used and is recommended where a more complete water insolubility is an important consideration. For a softer grease composition, potassium hydroxide may be used but it will increase cold water solubility. Any of these three metal hydroxides may be used to form the soap, reacting them preferably simultaneously with fatty acids or fatty oils in the conventional manner to form the soap in the grease. The soaps may be prepared separately, before addition to the grease, if desired, as will be obvious to those skilled in the art. The soap constituent may also be of alkaline earth metal base. such as calcium, strontium, or barium base, or it may be a mixed base soap comprising alkaline earth metal and alkali metal elements in its composition. The alkali metal soaps are preferred, however, and it is most convenient to used the same metal in the soap and in the sulfur-bearing salt.

In general, it is preferred to form the grease by first carrying out the Cannizzaro reaction, preferably in the presence of a portion, i. e., up to 35% of total lubricating oil employed, of relatively inert lubricating oil, a mineral oil of the desired viscosity being particularly preferred. After this, the fatty oil or fatty acid is added and is saponified with a suitable saponifying agent. A specifically preferred method comprises the reaction of 3 to 4 parts by weight of an alkali metal hydroxide with about 10 parts of a thiophene aldehyde, or a like aldehyde having a five membered thiophene or related heterocyclic sulfur-bearing ring structure in the presence of about 1 to 30 parts, preferably about 10 parts, of hydrocarbon oil. Thereafter, about to 25% by weight of C12 to C22 fatty material is added and is saponified with an approximately theoretical amount of saponifying agent such as alkali or alkaline earth metal oxide, hydroxide or carbonate, the alkali metal hydroxide being preferred. The fatty material is preferably a fatty acid or a mixture of fatty acids of the C15 to Cm range, but other fatty acids and/or glycerides may be used. The preferred method as suggested above is to use the same alkali metal oxide, carbonate or hydroxide for the Cannizzaro reaction and for the soap-forming reaction. When this is done, the use of an excess of the alkaline reagent in the Cannizzaro reaction is permissible, since such excess may be subsequently neutralized, or substantially neutralized, in the soap-forming reaction.

After the Cannizzaro reaction has been completed and the soap-forming ingredients are added, the composition is preferably heated to a grease-forming temperature of about 300 to 450 F. and the remainder of the lubricating oil is added as the temperature is raised. After cooking has been completed and the volatile ingredients, water, alcohol, to., have been substantially evaporated, the grease is cooled in a conventional manner, for example, by pan cooling, and is homogenized and packaged. In the case 4 of thiophene aldehyde, most of the alcohol, which is relatively non-volatile at usual grease cooking temperatures, remains in the grease as a modifying agent.

The preferred aldehyde for use in the Canm'zzaro reaction is alpha thiophene aldehyde but the homologous aldehydes and closely related heterocyclic aldehydes of the same general character may be used. For example, B-thiophene aldehyde may be used, as well as alpha thio-furfural HC--CH i is Related compounds containin small alkyl groups on the ring, for example, S-methyl or 5-methyl 2-thiophene aldehyde may also be employed.

Inasmuch as the resulting grease contains the sulfur of the thiophene molecule, and also in the usual case contains at least a small amount of the thiophene alcohol, polymerized or otherwise, the lubricating grease has appreciable extreme pressure properties which make it particularly useful where the unit loads on the parts to be lubricated are relatively high. In this respect, greases prepared from the thiophene aldehyde and related compositions have advantages not found in the furoic acid grease compositions of the parent application Serial No. 60,615.

The invention will be more fully understood by reference to the following specific example:

Per cent weight Sodium hydroxide 3.18 Mineral oil, 55 S. S. U. viscosity at 210 F. 10.00 Hydrofol Acids 54 (predominantly C18 substantially saturated fatty acids) Sodium hydroxide 1.00 Phenyl alpha naphthylamine 1.00 Mineral oil, as above 59.82

The thiophene aldehyde and a portion'of the mineral oil were charged to the grease kettle and stirring initiated. A 33 cold aqueous solution of sodium hydroxide (shown as part of the Cannizzaro reaction ingredients in the formulation) was then added. After completion of the Cannizzaro reaction, the Hydrofol Acids 54" were charged and neutralized with the balance of the sodium hydroxide aqueous solution). The balance of the mineral oil was added slowly while heating to 400 F. At this temperature the phenyl alpha naphthylamine was added as an oxidation inhibitor and the grease was cooled by pan cooling. It was further homogenized to a smooth uniform grease structure. The thiophene alcohol, as noted above, does not appear to form- Table Dropping "point, F 500+ 24 hour Cu corrosion test at ,210" F No corrosion or staining of a polished copper strip Norma-Hofiman bomb oxidation time (hours) to p. s. i. drop in pressure- P. s. 1. Hours 60 475 1500 Extreme pressure or load carrying properties as measured by the Shell 4-ball test Pressure wear index=23 The alpha thiophene aldehyde grease showed extreme pressure properties, essentially equivalent to conventional extreme pressure greases as measured by pressure Wear index tests. The pressure wear index test, employing the Shell 4- ball extreme pressure tester, consists of a determination of the average wear spot diameter of the test balls for each of a series of l-minute wear tests at various loads. The square of wear spot diameter is plotted against the applied load, using a log-log scale. The pressure wear index is defined as the quotient obtained by dividing the difference in load at the points of immediate and delayed seizure by the diiference in squares of the wear spot diameter at these points. The data are illustrated in the attached figure. The grease of the example showed a pressure wear index of 23 as compared with an index of 22 for a commercial extreme pressure grease of high quality containing 75% of extreme pressure additive. The latter grease without the extreme pressure additive showed a pressure wear index of only 6. Thus, the use of the sulfur-bearing aldehyde for the Cannizzaro reaction confers upon the grease extreme pressure properties substantially equal to those conferred bythe addition of as much as 7.5% of conventional extreme pressure additive. At the same time, this product has the exceptional properties of high temperature stability which appear to characterize the furfural type greases of the copending application mentioned above.

It will be understood that various modifications may be made in the process and in the product, and that conventional additives such as antioxidants, oiliness agents, tackiness or stringiness agents, metal deactivators, and the like, may be used, as is common practice in the art.

What is claimed is:

1. A lubricating grease composition having extreme pressure properties consisting essentially of a lubricatin oil thickened to a grease consistency with a combination of 1 to 3 molar parts of metal soap of higher fatty acids and 1 to 3 molar parts of the non-volatile Cannizzaro reaction products of an alkali metal hydroxide and a sulfur-containing heterocyclic aldehyde of molecular weight below about 200, said grease ineluding substantial amounts of the sulfurbearing alcohol formed in said (Janniz'zaro reaction'. 2. Alubricatin'g grease compositionhaving extreme pressure properties consisting essentially 'of a lubricating oil thickened toa grease consistency with acombination of l'to 3 molar'parts-of an alkali metalsoap offatty acid having between 12am 22 carbonatoms per molecule and -1 to '3 molar parts of thenon-volatile Cannizzaro reaction products of alkali metal hydroxide anda thiophene aldehyde, said grease including-substantial amounts of the sulfur-bearing alcohol formed in the Cannizzaro reaction.

3. Compositionaccording to claim2 wherein at least one of said alkali metals is sodium.

4. Composition according to claim 2 wherein at least one of said alkali metals is lithium.

5. Composition according to claim 2 wherein at least one of said alkali metals is potassium.

6. A lubricating grease composition having extreme pressure properties consisting essentially of lubricating oil containing 5 to 25% by weight, based on the total composition, of metal soap of C1: to C22 fatty acid, and about 3 to 15% of the non-volatile Cannizzaro reaction products of an alkali metal hydroxide with a sulfur-containing heterocyclic aldehyde, said aldehyde having a molecular weight below 200, said grease including substantial amounts of the sulfur-bearing alcohol formed in the Cannizzaro reaction.

7. The process of preparing a lubricating grease having extreme pressure properties which comprises reacting approximately 3 to 4 parts by weight of an alkali metal hydroxide with about 10 parts of a sulfur-containing heterocyclic aldehyde of molecular weight below about 200 in the presence of 1 to 30 parts of hydrocarbon oil whereby part of said aldehyde is converted to a heterocyclic carboxylic salt and part to the corresponding alcohol, thereafter adding 5 to 25 parts of C12 to C22 fatty material and saponifying with an alkali metal hydroxide, heating to a temperature of 300 to 450 F. and adding 30 to parts of mineral base lubricating oil during such heating, said grease being prepared under conditions such that substantial amounts of said alcohol remain therein.

8. Process according to claim 7 wherein at least one of the alkali metal hydroxides is sodium hydroxide.

9. Process according, to claim 7 wherein said aldehyde is a sulfur-bearing furfural compound.

10. Process according to claim 7 wherein at least one of the alkali metal hydroxides is lithium hydroxide.

11. Process according to claim 7 wherein at least one of the alkali metal hydroxides is potassium hydroxide.

12. Process according to claim '7 wherein said aldehyde is alpha thiophene aldehyde.

13. The process of preparing a lubricating grease having extreme pressure properties which comprises combining about 10 parts by weight of alpha thiophene aldehyde, 3 to 3.5 parts of sodium hydroxide and 10 parts of mineral lubricating oil, allowing the resulting Cannizzaro reaction to proceed substantially to completion, adding about 15 parts of substantially saturated higher fatty acids having an average of approximately 18 carbon atoms per molecule, adding sodium hydroxide in quantity substantially to saponify said fatty acid, adding about 60 parts of mineral lubricating oil and cooking to a temperature of between 300 and 450 F. until the volatile reaction products are substantially removed by evaporation and under conditions whereby substantial amounts of the sulfur-bearing alcohol formed in the Cannizzaro reaction remain in the grease.

14. A lubricating grease composition having extreme pressure properties consisting essentially of about 70 parts by weight of mineral base lubrieating oil, said oil being thickened to a grease consistency with the Cannizzarro reaction products of 10 parts by weight of alpha thiophene aldehyde and about 3.2 parts of sodium hydroxide, plus a soap formed from 15 parts of substantially saturated fatty acids of about 18 carbon atoms average chain length and 1 part of sodium '8 hydroxide said composition including substantial amounts of the sulfur-bearing alcohol formed in the Cannizzaro reaction.

' ARNOLD J. MORWAY. JOHN J. KOLFENBACH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. A LUBRICATING GREASE COMPOSITION HAVING EXTREME PRESSURE PROPERTIES CONSISTING ESSENTIALLY OF A LUBRICATING OIL THICKENED TO A GREASE CONSISTENCY WITH A COMBINATION OF 1 TO 3 MOLAR PARTS OF METAL SOAP OF HIGHER FATTY ACIDS AND 1 TO 3 MOLAR PARTS OF THE NON-VOLATILE CANNIZZARO REACTION PRODUCTS OF AN ALKALI METAL HYDROXIDE AND A SULFUR-CONTAINING HETEROCYCLIC ALDEHYDE OF MOLECULAR WEIGHT BELOW ABOUT 200, SAID GREASE IN 